1. Field of the Invention
The present invention relates to an optical signal receiver, an optical signal monitoring unit, and an optical signal monitoring method, and more particularly to the optical signal receiver having a function of monitoring optical signals according to a bit rate of an input signal, to the optical signal monitoring unit making up the optical signal receiver, and the optical signal monitoring method without depending on bit rate information.
The present application claims priority of Japanese Patent Application No. 2005-082613 filed on Mar. 22, 2005, which is hereby incorporated by reference.
2. Description of the Related Art
Conventionally, in an optical transmission system, various transmission path networks having different specifications are employed and bit rates to be used for transmission are various. For example, a plurality of types of transmission networks is employed for transmission, which includes a SONET (Synchronous Optical Network)/SDH (Synchronous Digital Hierarchy) network, FC (Fiber Channel) network, GbE (Gigabit Ethernet) network, or a like. Therefore, in an optical signal transmitter and an optical signal receiver serving as signal transmission devices connected through a transmission path using an optical fiber, for example, it is made necessary to use a device designed specifically for every bit rate.
As shown in FIG. 6, for example, in the SONET/SDH network, an optical signal transmitter 102 for the SONET/SDH network and an optical signal receiver 103 for the SONET/SDH network are connected to each other through a transmission optical fiber 101. In the GbE network, an optical signal transmitter 105 for the GbE network and an optical signal receiver 106 for the GbE network are connected to each other through a transmission optical fiber 104. In the FC network, an optical signal transmitter 108 for the FC network and an optical signal receiver 109 are connected to each other through a transmission optical fiber 107.
Each of the optical signal receivers 103, 106, and 109 has a function of monitoring optical communications, which includes a photoelectric converting circuit 202 to convert an input optical signal into an electrical signal, a clock/data regenerating circuit 203 to extract a clock signal, based on the input electrical signal, to identify a data signal and to regenerate the data signal, and a performance monitoring circuit 204 to receive the clock signal and data signal from the clock/data regenerating circuit 203 and to monitor alarm information. In each performance monitoring circuit 204 included in each of the optical signal receivers, an operation of detecting the alarm information differs depending on, for example, every specification corresponding to a bit rate and, therefore, the optical signal receivers cannot be used in a shared manner.
For example, in the SONET/SDH network, in order to achieve effective signal transmission, an overhead used to transfer operation and maintenance information (error monitoring signal, alarm transferring signal, synchronization signal) is predetermined and, by using the overhead, a parity check called a “Bit Interleaved Parity” is made among repeaters or among multiplexing terminal stations to identify a failure section.
In response to demands of a recent multi-media service providing market and in order to perform such the diversified transmission methods as described above, a conventional optical signal receiver being able to receive signals irrespective of types of adopted protocols (bit rates) is disclosed in Patent Reference 1 (Japanese Patent Application Laid-open No. 2001-053814) and Patent Reference 2 (Japanese Patent Application Laid-open No. 2003-509927). In these conventional optical signal receivers, when alarm information contained in a transmitted signal is to be extracted from a data signal regenerated by a clock/data regenerating circuit, optical signal receivers each having a different performance monitoring circuit that can correspond to a different bit rate must be prepared, thus making configurations expensive and complicated.